1. Field of the Invention
This invention relates to an oscillation circuit, an electronic circuit using that oscillation circuit, and a semiconductor device, electronic equipment, and timepiece using that oscillation circuit or electronic circuit.
2. Description of the Related Art
Oscillation circuits that use crystal oscillators are widely employed in the art in devices such as portable timepieces, portable telephones, and computer terminals. It is necessary to design such portable items of electronic equipment in such a manner that they are economical in their power consumption and have longer battery lives.
This crystal oscillation circuit comprises an inverting amplifier and a feedback circuit that is provided with a crystal oscillator. The inverting amplifier comprises a pair of transistors where the gate of each of these transistors is used as an input side and the drain thereof is used as an output side, by way of example. In this case, the drain sides of these two transistors are connected together and the source sides thereof are connected to ground and a power voltage side, respectively.
If the power voltage is applied to the inverting amplifier in the crystal oscillation circuit of this configuration, the phase of the output of the inverting amplifier is inverted through 180 degrees and the thus inverted signal is fed back to the gate of each transistor as an input. The transistors configuring the inverting amplifier are turned on and off alternately by the operation of this feedback, the oscillation output of the crystal oscillation circuit gradually increases, and thus the oscillator starts to oscillate stably.
However, the absolute value of a voltage Vreg applied to the inverting amplifier in this prior-art crystal oscillation circuit is set to be greater than the total of the absolute values of the threshold voltages VTP and VTN of the transistors in this circuit, as follows:
|Vreg| greater than |VTP|+|VTN|xe2x80x83xe2x80x83(1)
The current inventors have discovered that this is the cause of a short-circuiting current IS that flows from the high potential side to the low potential side within the inverting amplifier, which causes a problem when trying to reduce the power consumption of the entire circuit.
An objective of this invention is to reduce the above short-circuiting current that flows through the inverting amplifier and thus provide an oscillation circuit that can oscillate with a low power consumption, an electronic circuit that uses such an oscillation circuit, and a semiconductor device, electronic equipment, and timepiece that use this oscillation circuit or electronic circuit.
In order to achieve the above objective, an oscillation circuit in accordance with a first aspect of this invention comprises an inverting amplifier including a first semiconductor switching element and a second semiconductor switching element;
wherein the first and second semiconductor switching elements are prevented from being on simultaneously to limit a short-circuiting current flowing through the inverting amplifier when the first and second semiconductor switching element is driven.
This configuration makes it possible to limit the short-circuiting current flowing through the inverting amplifier, making it possible to provide an oscillation circuit that can oscillate with a low power consumption.
The sum of the absolute value of the threshold voltage of the first semiconductor switching element and the absolute value of the threshold voltage of the second semiconductor switching element may be set to be greater than or equal to the absolute value of the power voltage of the inverting amplifier, to limit a short-circuiting current flowing through the inverting amplifier.
The oscillation circuit of this invention may further comprise a feedback circuit having a crystal oscillator connected between the output and input sides of the inverting amplifier, for causing the phase of an output signal from the inverting amplifier to invert and feeding the thus inverted signal back to the inverting amplifier as an input;
wherein the inverting amplifier comprises a first circuit including the first semiconductor switching element, and a second circuit including the second semiconductor switching element;
wherein the first semiconductor switching element is connected to the side of a first potential and is driven to be turned on and off by the feedback input, to excite the crystal oscillator;
wherein the second semiconductor switching element is connected to the side of a second potential that differs from the first potential and is driven to be turned on and off by the feedback input at a timing that differs from that of the first semiconductor switching element, to excite the crystal oscillator; and
wherein the sum of the absolute value of the threshold voltage of the first semiconductor switching element and the absolute value of the threshold voltage of the second semiconductor switching element is set to be greater than or equal to the absolute value of the power voltage of the inverting amplifier, to limit a short-circuiting current flowing through the inverting amplifier.
In this case, when a voltage is applied to the inverting amplifier in the crystal oscillation circuit, excitation of the crystal oscillator starts. The phase of the output of the inverting amplifier is inverted by the feedback circuit and is fed back as an input. The operations of inverting, amplifying, and outputting this feedback input signal by the inverting amplifier are repeated.
During this time, the first and second semiconductor switching elements that configure the inverting amplifier are driven to be turned on and off at mutually different timings by this feedback input, to excite the crystal oscillator.
As stated above, the sum of the absolute values of the threshold voltages of the first and second semiconductor switching elements can be set to be greater than or equal to the absolute value of the power voltage of the inverting amplifier. This prevents the first and second semiconductor switching elements from being driven to turn on simultaneously when the circuit is operating, and, as a result, the short-circuiting current flowing through the inverting amplifier can be greatly reduced, making it possible to reduce the power consumption.
In particular, by forming the first and second transistors in such a manner that the threshold voltage conditions are satisfied, there is no further need for means for dealing with this short-circuiting current, making it unnecessary to use special circuit components for counteracting this short-circuiting current. This makes it possible to reduce the power consumption of the crystal oscillation circuit without adversely affecting the degree of integration of the entire circuit.
Note that it is necessary to set each of the absolute values of the threshold voltages of these first and second semiconductor switching elements to be less than the absolute value of the power voltage of the inverting amplifier.
The oscillation circuit may further comprise a bias circuit for applying a first direct current bias voltage and a second direct current bias voltage to gates of the first semiconductor switching element and the second semiconductor switching element, respectively;
wherein the first and second direct current bias voltages shift the values of the direct current potentials of feedback inputs that are input from the inverting amplifier to the gates of the first and second semiconductor switching elements, to prevent the first and second semiconductor switching elements from being on simultaneously.
The oscillation circuit may further comprise:
a feedback circuit having a crystal oscillator connected between the output and input sides of the inverting amplifier, for causing the phase of an output signal from the inverting amplifier to invert and feeding the thus inverted signal back to the inverting amplifier as an input; and
a bias circuit for applying a direct current bias voltage to the inverting amplifier;
wherein the inverting amplifier comprises:
a first circuit connected to the side of a first potential and comprising the first semiconductor switching element; and
a second circuit connected to the side of a second potential that differs from the first potential and comprising the second semiconductor switching element;
wherein the first semiconductor switching element is connected to the side of the first potential and is driven to be turned on and off by the feedback input that is input to a gate, to excite the crystal oscillator;
wherein the second semiconductor switching element is connected to the side of the second potential and is driven to be turned on and off by the feedback input that is input to a gate at a timing that differs from that of the first semiconductor switching element, to excite the crystal oscillator;
wherein the bias circuit comprises:
a first bias circuit for applying a first direct current bias voltage to the gate of the first semiconductor switching element; and
a second bias circuit for applying a second direct current bias voltage to the gate of the second semiconductor switching element; and
wherein the first and second direct current bias voltages shift the values of the direct current potentials of feedback inputs that are input from the inverting amplifier to the gates of the first and second semiconductor switching elements, to prevent the first and second semiconductor switching elements from being on simultaneously.
By employing the above configuration, there is no common-on time at which both of the first and second semiconductor switching elements are on, while the first and second semiconductor switching elements that configure the inverting amplifier are driven to be turned on and off at mutually different timings by this feedback input, to excite the crystal oscillator. Therefore the short-circuiting current flowing through the inverting amplifier can be greatly reduced, making it possible to achieve a crystal oscillation circuit that can oscillate stably at a low power consumption.
In particular, the short-circuiting current of the inverting amplifier can be reduced, even when the absolute values of the threshold voltages of the first and second semiconductor switching elements are made small. The power voltage of the crystal oscillation circuit can therefore be reduced by that amount, making it possible to reduce the power consumption of the oscillation circuit even further.
In this case, the first direct current bias voltage may be set to the first potential and the second direct current bias voltage may be set to the second potential.
The direct current potentials of the inputs fed back to the gates of the first and second semiconductor switching elements can be shifted towards the respective first and second potential sides of the power source by the application of the thus-set direct current bias voltages. This makes it possible to provide a crystal oscillation circuit which has a simple circuit configuration and which can reduce the short-circuiting current of the inverting amplifier.
The first and second semiconductor switching elements may be configured by using field-effect transistor elements of differing conductivity types.
According to a second aspect of this invention, there is provided an electronic circuit comprising the above oscillation circuit of this invention.
Similarly, according to a third aspect of this invention, there is provided a semiconductor device comprising one of the above oscillation circuit and the electronic circuit of this invention.
Furthermore, according to a fourth aspect of this invention, there is provided electronic equipment comprising one of the above oscillation circuit and the electronic circuit of this invention.
This can reduce the power consumption of an item of portable electronic equipment, such as a portable telephone or computer terminal, and thus makes it possible to reduce the consumption thereof of power from an internal battery or secondary battery.
Finally, according to a fifth aspect of this invention, there is provided a timepiece comprising one of the above oscillation circuit and the electronic circuit of this invention.
This makes it possible to implement a portable timepiece that has a low power consumption, which enables the design of a timepiece that is itself smaller and uses an even smaller battery. Alternatively, the battery life thereof could be extended even when a battery of the same capacity is used.